According to Bard, “the purpose of prohibitions on evidence is to ensure the reliability of knowledge and, above all, to prevent the conviction of an innocent person.”1 The author adds, however, that these rules are also intended to protect other “substantive values” whose function is primarily to protect the fundamental rights of the person charged.2

The purpose of procedural sanctions is to enforce the procedural conduct of the persons subject to the proceedings, that is to say, to enforce the conduct of the subjects of the proceedings in accordance with the rules of procedural law. Indeed, in many cases, the members of the public authority regard these sanctions as a “harmful rule which condemns the procedure to failure”.3 By contrast, prohibitions on taking evidence are intended to ensure, together with other rules of evidence, a fair and transparent procedure.4 This is both positive and problematic from the point of view of due process, because a rule which favours the accused is not necessarily in the public interest of law enforcement, or the victim, who is disappointed in the criminal proceedings if the accused escapes criminal sanctions because he cannot be forced to make a self-incriminating confession or because it is prohibited to prove his guilt. 5

A question worth considering arises how far can and should we go with prohibitions on evidence to protect the rights of the accused but not to make prosecution impossible? The Court of Justice has consistently held that it is for the Member States to define these standards, and the forum has in several cases pointed to its lack of competence to decide on the admissibility of illegally obtained evidence in court. Accordingly, the use of illegally obtained evidence cannot, in principle, be excluded.6

If such evidence is of little relevance to the exercise of that fundamental procedural right, no violation of the Convention may be established.7

The prohibitions on obtaining evidence are primarily rules of conduct for investigating authorities and prosecutors (regardless of the nature of the legal system). Most of the issues relate to their admissibility in court. According to some authors, “the most important task of procedural law is precisely to develop and establish rules to ensure that the methods of taking evidence are as pure and ethical as possible and that the evidence used to ensure the objectivity and impartiality of the judicial decision is as reliable and free from error as possible.”8 The regulation of these limitations, based in particular on the principle of the rule of law, has thus become a fundamental requirement of all modern procedural codes.9 As a general principle, it can be established that facts derived from an instrument of evidence obtained by the proceeding authority (court) by means of a criminal offence, other prohibited means or by substantially limiting the procedural rights of the participants cannot be admissible as evidence.

Another question worth considering is: what criteria should be used to determine these prohibition rules? I consider the primary guiding principle to be that these rules must be precisely defined in the relevant procedural code so that the possibility of “judicial arbitrariness” is not even minimally present in the case of decisions on evidentiary acts and motions. The discretionary power of the public (judicial) authorities may at most be limited to preventing the proof of facts which are manifestly impossible, absurd or cannot be proved by empirical-scientific methods.10

According to Király, the procedural law should define directly and precisely the acts that are prohibited. It seems better and more appropriate for the procedural code to contain specific prohibitions on some methods of proof (e.g. torture, exhaustion, hypnosis, stunning, illicit coercion), even if the Criminal Code includes such offences as coercive interrogation and others. The CPC should decide on this issue independently. In this context, the norms of the acts of proof and the consequences of their violation should be formulated in the Code in a regulated manner.11

Some views, however, argue that it would be sufficient to prohibit only those acts of proof which are also criminal offences or contrary to the principles of the CPC. Such considerations, however, carry many dangers, since they only provide a broad framework for the prohibition, which could lead to serious abuses and errors of law enforcement.12 Just think of the impossible situation that would result if the principle of fair trial were enshrined in the basic system of the CPC. I wonder how many defence motions would be brought in a given proceeding on the basis of this principle because the authorities have violated or restricted the rights of the accused.

I would also note here, however, that “tactical bluffing” can hardly be prohibited. As the Court of Justice has pointed out in an earlier decision, it is not necessarily illegal in itself for the police to resort to various tricks to prevent crime more effectively.13 Of course, the principles established by law and judicial practice (e.g. the prohibition of using leading questions, etc.) also apply to such cases, but the mental exhaustion of witnesses, the “exaggeration” of the professional responsibility of an expert in public by his or her defence, etc., can hardly fall into this category.

As regards the method of detecting procedural irregularities, there are two basic models:

The CPC follows the principle of the so-called “silver platter”, according to which illegally obtained evidence cannot be evaluated as such, but the information derived from it can be used in the further part of the proceedings. Following the example of Háger, “if […] a confession is extorted from an accused person by threat, his confession cannot be incriminating, but there is no obstacle to the inclusion of the material evidence obtained from the confession in the scope of evaluation.” 15

The Court found a violation of the Convention when the criminal liability of a person accused of drug trafficking was established solely on the basis of evidence obtained illegally by the police with the help of secret listening devices. The British courts rejected the defendant’s appeal on this point, on the ground that, in the present case, the State’s criminal claim was based on an interest greater than respect for the right to privacy. Nevertheless, the Court found a violation of Article 8 of the Convention, since it found that the Hungarian legislation on the use of secret service agents was inadequate, and, since the right to an effective remedy was also restricted, it also found a violation of Article 13. In the Court’s view, the accused would have had several opportunities to object to the evidence in the main case, but his complaints related only to the fact of its use.16

The Court did not find a breach of the Convention when